JP5359796B2 - Method for producing SiC single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an SiC single crystal, by which SiC having stable quality can be produced for a long time by a solution method. <P>SOLUTION: The method for producing an SiC single crystal comprises growing an SiC single crystal on an SiC seed crystal substrate 9 from a raw material solution 3 containing SiC, C and a solution component other than the two components by the solution method, and includes a process for dissolving C before the start of SiC growth and a process for replenishing SiC after the start of SiC growth. In the process for replenishing SiC, SiC is replenished from a shielding wall 4 made of SiC, provided between a support rod 5 of the SiC seed crystal substrate 9 and a graphite crucible 2, in the solution 3. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

The present invention relates to a method for producing a SiC single crystal, and more specifically, in a method for producing a SiC single crystal by a solution method, SiC having a stable quality is obtained from a solution containing Si, C and another component (X) after the start of SiC growth. The present invention relates to a method for producing a SiC single crystal that can be produced for a long time.

  SiC single crystals are very thermally and chemically stable, excellent in mechanical strength, resistant to radiation, and have excellent physical properties such as higher breakdown voltage and higher thermal conductivity than Si. In addition, it is easy to control p and n conduction type electrons by adding impurities, and a wide forbidden band width (about 3.0 eV for 6H type single crystal SiC and about 3.3 eV for 4H type single crystal SiC). It has the feature of having. Therefore, it is possible to realize high temperature, high frequency, withstand voltage / environment resistance that cannot be realized with existing semiconductor materials such as silicon (Si) and gallium arsenide (GaAs). Yes.

Conventionally, as a method for growing a SiC single crystal, a gas phase method, an Acheson method, and a solution method are typically known.
Of the sublimation method and chemical vapor deposition (CVD), which are typical examples of the vapor phase method, the sublimation method causes various defects in the crystal and is easily polycrystallized, and the CVD method limits the supply of raw materials to gas. The produced crystal is a thin film, and it is difficult to produce a bulk single crystal.
In addition, since the Atchison method uses silica and coke as raw materials and heats them in an electric furnace, it cannot be highly purified due to impurities in the raw materials.

The solution method is a method in which an alloy containing alloy is melted in a graphite crucible, carbon is dissolved in the melt from the graphite crucible, and a SiC crystal layer is grown on the seed crystal substrate placed in a low temperature part by solution precipitation. . The solution method is known to be advantageous as a method for obtaining a bulk single crystal although the growth rate is low. For this reason, various studies have been made to increase the growth rate of the SiC single crystal growth method by the solution method that does not have the above-mentioned problems in the gas phase method or the Atchison method.
On the other hand, various studies for obtaining a single crystal safely and with stable quality have been made.

For example, in Patent Document 1, when a single crystal was grown by the CZ method (Czochralski Method), an initial charge was made in the crucible in order to charge the polycrystalline raw material statically and stably in the crucible. A cylindrical container filled with a bulk and / or granular polycrystalline raw material is installed above the polycrystalline raw material, and the polycrystalline raw material in the cylindrical container is removed as the polycrystalline raw material in the crucible is dissolved. A CZ raw material supply method for additionally supplying into the crucible is described. As a specific example, a production example of a silicon single crystal is described.
In Patent Document 2, a solution component other than Si and C of 5 to 30 at% Ti and 1 to 20 at% Sn or 1 to 30 at% Ge is added to the Si melt in the graphite crucible, A method for producing a SiC single crystal that promotes dissolution of C in a graphite crucible is described.

JP 2003-020295 A JP 2008-303125 A

According to the method for producing a single crystal described in each of the above patent documents, it is said that a single crystal can be stably obtained. However, by any method, a SiC single crystal is continuously grown with a stable quality by a solution method for a long time. It is difficult.
Accordingly, an object of the present invention is to provide a method for producing a SiC single crystal capable of producing SiC of stable quality for a long time by a solution method.

As a result of examining the manufacturing method of the SiC single crystal by the solution method, the present inventors have found that, in the growth of the SiC single crystal by the conventional solution method, C is dissolved from the graphite crucible while Si is consumed. As a result of further investigation, it was found that the change in the concentration of each component in the solution with time alone is one of the causes that make it difficult to continue growing a SiC single crystal with a stable quality for a long time. Completed the invention.
The present invention is a method for growing a SiC single crystal on a SiC seed crystal substrate from a raw material solution containing Si, C, and solution components other than the two components by a solution method, wherein C is dissolved before the start of SiC growth. A step of replenishing SiC from a SiC shielding wall provided in the solution and between the support rod of the SiC seed crystal substrate and the graphite crucible after the start of SiC growth. The present invention relates to a method for producing a SiC single crystal.

  According to the present invention, it is possible to easily produce a SiC single crystal having a stable quality for a long time by a solution method.

FIG. 1 is a copy of a surface photograph of a grown crystal when a SiC single crystal is grown from a Si—C—X solution containing SiC, C, and solution components other than the two components by the solution method of the prior art. FIG. 2 is a partial schematic view showing an embodiment of the present invention.

In the present invention, by a solution method, a method of growing an SiC single crystal SiC seed crystal substrate from a raw material solution containing solution components X other than the two components Si and C, before the start SiC growth C It is possible to manufacture a SiC single crystal having a stable quality for a long time by a method for manufacturing a SiC single crystal having a step of dissolving SiC and having a step of supplying SiC after the start of SiC growth.
In the above description, the fact that a SiC single crystal of stable quality can be produced for a long time means that the growth time in the SiC crystal growth by a normal solution method, for example, a time longer than 2 hours is flat on the SiC seed crystal substrate. This means that the three-dimensional growth due to the polycrystallization of the surface properties can be reduced or the SiC single crystal can be produced without the three-dimensional growth.

Hereinafter, the present invention will be described with reference to FIGS.
As shown in FIG. 1, when a SiC single crystal was grown on a SiC seed crystal substrate at 2000 ° C. using a Si—C—X solution according to the prior art, the growth started as shown in FIG. The crystal surface photograph after 2 hours shows that a high-quality SiC single crystal having a flat surface property was obtained. A crystal surface photograph 8 hours after the start of growth shown in FIG. 1B shows that three-dimensional crystal growth has occurred. This is considered to be due to the fact that Si in the Si-C-X solution decreases with growth and the composition ratio of X to Si fluctuates, resulting in polycrystallization and three-dimensional growth.

  This is because, in the growth method of the SiC single crystal according to the prior art in the solution method, X which is a component other than Si and C is added to promote the dissolution of C from the graphite crucible, and with the progress of the growth of the SIC single crystal Si decreases, that is, the composition ratio of the solvent component X to Si increases. Then, the composition ratio of X with respect to Si deviates from the SiC stable precipitation region and becomes polycrystalline, so that stable growth cannot be performed. Growth capable of providing a single crystal is possible, but growth capable of providing a high-quality SiC single crystal cannot be achieved over time.

As shown in FIG. 2, in the embodiment of the present invention, the Si—C—X solution 3 (from the graphite crucible 2 installed in the reaction vessel 1 before the C saturation in the left diagram, and thus before the start of the SiC growth, ( C is dissolved in the C concentration is less than the saturation concentration), and after S saturation in the right figure, after SIC growth starts, SiC is replenished from ring-shaped SiC 4 immersed in the inside of the graphite crucible 2 in the solution. By keeping the ratio of C constant, the composition ratio of X to Si does not deviate from or extremely less than the SiC stable precipitation region, so that stable growth is possible and a stable quality SiC single crystal can be obtained for a long time. Can be manufactured.

The ring-shaped SiC 4 is a ring-shaped SiC made of single-crystal or polycrystalline SiC before C saturation in the left diagram of FIG. 2, and thus before the start of SiC growth, and moves the graphite rod 5 up and down. The main part 7 of ring-shaped SiC is fixed to the support part 6 for causing the bottom part 8 to be disposed at the bottom of the graphite crucible, and when C in the right figure of FIG. After the graphite rod 5 is lowered so that the SiC single crystal substrate 9 bonded to the solution comes into contact with the solution surface and the SiC growth starts, the main portion 7 of the ring-shaped SiC and the bottom portion 8 of the ring-shaped SiC are integrated. As described above, the position of the support 6 and the shape and position of the bottom 8 need to be configured and arranged in advance. The bottom portion 8 is preferably made of SiC, and the shape thereof may be any shape such as a flat shape or an arc shape as long as the space of the ring-shaped SiC main portion 7 can be filled. Further, SiC that provides ring-shaped SiC 4 may be manufactured by any manufacturing method.

  In the present invention, the raw material solution for growing the SiC single crystal is one or more components that promote the dissolution of Si, C, and C from the graphite crucible and / or components that are added from the viewpoint of the quality of the grown crystal. An arbitrary solution containing X, which is a component consisting of these elements, as an essential component can be mentioned, for example, as a raw material solution, containing X and Ti and / or Cr as an X, for example, elements other than Si, Cr and C And those containing any one element selected from rare earth elements, transition metal elements and alkaline earth elements. X is 5 to 50 at. %.

The raw material solution may have a solution temperature in the range of 1600 to 2100 ° C., for example, in the range of 1800 to 2100 ° C.
The temperature of the raw material solution is controlled by, for example, heating by high frequency induction heating, for example, observation of the temperature of the raw material solution surface by a radiation thermometer and / or a thermocouple installed inside the carbon rod, for example, W-Re (tungsten / renium) The temperature can be measured by a temperature controller based on the measured temperature obtained by measuring the temperature using a thermocouple.

In the method for producing SiC by the solution method of the present invention, the conditions in the crucible before the start of crystal growth and after the start of crystal growth, such as the shape, atmosphere, heating method, heating time, heating rate and cooling rate of the graphite crucible It can be performed by appropriately selecting the optimum conditions from the conventionally known conditions in the method.
For example, although it depends on the size of the crucible, the heating time by high frequency induction heating (the approximate time from the preparation of the raw material until reaching the SiC saturation concentration) is 20 minutes or more, for example, about 20 minutes to 10 hours (for example, 3 to 8 hours). The atmosphere may be a rare gas, for example, an inert gas such as He, Ne, or Ar, or a mixed gas of the inert gas and N ₂ or methane gas.

  By the SiC single crystal growth by the solution method in the present invention, a SiC single crystal is grown at a high temperature for a long time, for example, longer than 2 hours, for example, longer than 5 hours, while preventing or suppressing the growth of polycrystals. obtain.

  Hereinafter, although an example and a comparative example are given and the present invention is explained more concretely, the present invention is not limited to the following examples.

Comparative Example 1
According to the conventional technique, a SiC single crystal was grown on a SiC seed crystal substrate at 2000 ° C. using a Si—C—X (Ni or Cr) solution. A crystal surface photograph 2 hours after the start of growth and a crystal surface photograph 8 hours after the start of growth are shown in FIGS.
FIG. 1 shows that a high-quality SiC single crystal having a flat surface property was obtained 2 hours after the start of growth, but three-dimensional crystal growth occurred 8 hours after the start of growth. Yes.

Example 1
A raw material having the composition shown in Table 1 was added, and the amount of SiC shown in Table 1 was replenished after the start of growth by a Si—C—X (Ni or Cr) solution method, and the effect was simulated. The results are shown in Table 1.

As shown in Table 1, C was dissolved before the start of crystal growth, and SiC was replenished at the stage after the start of SiC growth after C reached the saturation concentration. The composition ratio at the start of SiC growth: X / (Si + X) = 20 (%), the same as the composition ratio after replenishment of SiC: X / (Si + X) = 20 (%), and there is no change in the composition ratio.
This is because when SiC is immersed after C saturation, SiC dissolves as much as C is unsaturated, so that Si, C, and X can always be maintained in the same amount and in the same composition ratio. This shows that stable crystal growth is possible for a long time.

Comparative Example 2
The raw material having the composition shown in Table 2 was added, and the solvent raw material was added by the Si—C—X (Ni or Cr) solution method, and the effect was simulated. The results are shown in Table 2.

  As shown in Table 2, C was dissolved before the start of crystal growth, and Si was replenished at the stage after the start of SiC growth. When only Si is replenished, it is a problem if it is too much or too little, and it is necessary to replenish Si in the same amount as the amount grown, and control is difficult. In addition, since the melting point of Si is low, the amount to be charged must be controlled in a solid state, which makes it difficult to perform the charging operation, and it is difficult to easily perform stable crystal growth.

Comparative Example 3
A simulation was performed in which SiC and X (for example, Cr or Ni) were added to the heat-resistant container from the beginning, and SiC was sequentially added as shown in Table 3. The results are shown in Table 3.

  As shown in Table 3, when SiC is replenished, the composition ratio: X / (Si + X) decreases to 20 (%), 19 (%), and 18 (%), and the saturation C also varies. That is, it is shown that it is difficult to perform stable crystal growth by the method of adding SiC from the beginning.

  According to the method of the present invention, a stable quality SiC single crystal is grown for a long time from a solution containing Si, C and other component (X) after the start of SIC growth in a method for producing an SiC single crystal by a solution method. It becomes possible.

DESCRIPTION OF SYMBOLS 1 Reaction container 2 Graphite crucible 3 Si-C-X solution 4 Ring-shaped SiC
5 Graphite rod 6 Supporting part 7 Ring-shaped SiC main part 8 Ring-shaped bottom part 9 SiC single crystal substrate 10 Heat insulating material

Claims (1)

A method of growing a SiC single crystal on a SiC seed crystal substrate from a raw material solution containing Si, C, and solution components other than the two components by a solution method, comprising a step of dissolving C before the start of SiC growth. The SiC single crystal is characterized by having a step of replenishing SiC from a SiC shielding wall provided in the solution between the support rod of the SiC seed crystal substrate and the graphite crucible after the start of SiC growth. Production method.